1. Field of the Invention
The present invention relates generally to a color laser display of a type where a screen is scanned with three-color laser light, and more particularly to a color laser display in which an excitation solid laser unit with a Pr3+-doped solid-state laser crystal, or a fiber laser unit with a fiber having a Pr3+-doped core, or a semiconductor laser unit with a GaN semiconductor laser element for exciting a surface-emitting semiconductor element, is employed as a laser light source.
2. Description of the Related Art
There is a conventional color laser display in which an image is projected onto a screen, which displays each color when irradiated with red, green, and blue light, by scanning the screen with laser light modulated based on each color image signal. In another conventional color laser display, an image obtained by modulating laser light with a spatial modulation element is projected onto a screen by a projection optics system. These types of color laser displays require a laser light source, whose output is of the order of W (watt), in order to meet the high-brightness requirement. Because of this, a high-output gas laser, such as an Ar+ gas laser, a Kr+ gas laser, etc., has been used as the laser light source. However, the gas laser has the disadvantage that its device size is increased and manufacturing costs are considerably high, because the energy conversion efficiency is low such as about 0.1% and a cooling mechanism is necessary.
Hence, excitation second-harmonic-generation (SHG) solid lasers have recently been used as visible short-wavelength laser light sources, as described in Jpn. J. Laser Focus World, p.52 (December 1997). For instance, an yttrium aluminum garnet (YAG) laser unit, which employs an excitation solid laser element of oscillating wavelength 1064 nm to emit laser light of green wavelength 532 nm, is higher in energy conversion efficiency than the aforementioned gas laser.
However, noise due to a conflict of longitudinal modes will occur as the aforementioned excitation SHG laser unit generates higher output. For example, Jpn. J. Laser Focus World (p 243, May 1998) discloses that an amount of noise due to the blue and green solid laser elements is 3% or less, while an amount of noise due to the red solid laser element is as much as 50%.
To control these longitudinal modes, it is conceivable to insert, for example, an etalon as a wavelength selecting element. However, in such a case, realization of perfect single mode oscillation results in a great loss in efficiency, and consequently, high output is no longer obtainable and there arises a problem that the laser display will not able to have high brightness. Thus, in the case of employing the excitation SHG solid laser unit as a light source for a laser display, a reduction in the size is attainable, but numerous problems remain unsolved with respect to high efficiency, device performance, and costs.
The present invention has been made in view of the problems found in the prior art. Accordingly, it is the primary object of the present invention to provide a color laser display that is capable of realizing size reduction, high efficiency, and noise reduction.
To achieve this end and in accordance with an important aspect of the present invention, there is provided a first color laser display comprising:
a red laser light source for emitting red laser light;
a green laser light source for emitting green laser light;
a blue laser light source for emitting blue laser light;
modulation means for modulating the red laser light, the green laser light, and the blue laser light, based on a red image signal, a green image signal, and a blue image signal;
a screen for displaying red, green, and blue when irradiated with the red laser light, the green laser light, and the blue laser light; and
projection means for projecting the red laser light, the green laser light, and the blue laser light onto the screen so that an image, carrying the red, green, and blue image signals, is displayed on the screen;
wherein an excitation solid laser unit, having a solid-state laser crystal doped with Pr3+ and a GaN semiconductor laser element for exciting the solid-state laser crystal, is employed as at least one of the red laser light source, the green laser light source, or the blue laser light source.
In the first color laser display, the excitation solid laser unit may emit laser light of wavelength 600 to 660 nm by a transition of 3P0xe2x86x923F2 or 3P0xe2x86x923H6, and this laser unit can be satisfactorily employed as the red laser light source. The excitation solid laser unit may also emit laser light of wavelength 515 to 555 nm by a transition of 3P1xe2x86x923H5, and this laser unit can be satisfactorily employed as the green laser light source. Furthermore, the excitation solid laser unit may emit laser light of wavelength 465 to 495 nm by a transition of 3P0xe2x86x923H4, and this laser unit can be satisfactorily employed as the blue laser light source.
In accordance with another important aspect of the present invention, there is provided a second color laser display comprising:
a red laser light source for emitting red laser light;
a green laser light source for emitting green laser light;
a blue laser light source for emitting blue laser light;
modulation means for modulating the red laser light, the green laser light, and the blue laser light, based on a red image signal, a green image signal, and a blue image signal;
a screen for displaying red, green, and blue when irradiated with the red laser light, the green laser light, and the blue laser light; and
projection means for projecting the red laser light, the green laser light, and the blue laser light onto the screen so that an image, carrying the red, green, and blue image signals, is displayed on the screen;
wherein a fiber laser unit, having a fiber with a Pr3+-doped core and a GaN semiconductor laser element for exciting the fiber, is employed as at least one of the red laser light source, the green laser light source, or the blue laser light source.
As with the first color laser display, the excitation solid laser unit of the second color laser display may emit laser light of wavelength 600 to 660 nm by a transition of 3P0xe2x86x923F2 or 3P0xe2x86x923H6, and this laser unit can be satisfactorily employed as the red laser light source. In addition, the excitation solid laser unit of the second color laser display may emit laser light of wavelength 515 to 555 nm by a transition of 3P1xe2x86x923H5, and this laser unit can be satisfactorily employed as the green laser light source. Furthermore, the excitation solid laser unit of the second color laser display may emit laser light of wavelength 465 to 495 nm by a transition of 3P0xe2x86x923H4, and this laser unit can be satisfactorily employed as the blue laser light source.
In accordance with still another important aspect of the present invention, there is provided a third color laser display comprising:
a red laser light source for emitting red laser light;
a green laser light source for emitting green laser light;
a blue laser light source for emitting blue laser light;
modulation means for modulating the red laser light, the green laser light, and the blue laser light, based on a red image signal, a green image signal, and a blue image signal;
a screen for displaying red, green, and blue when irradiated with the red laser light, the green laser light, and the blue laser light; and
projection means for projecting the red laser light, the green laser light, and the blue laser light onto the screen so that an image, carrying the red, green, and blue image signals, is displayed on the screen;
wherein a semiconductor laser unit is employed as at least one of the red laser light source, the green laser light source, or the blue laser light source, and the semiconductor laser unit includes an excitation light source constructed of a semiconductor laser element employing a GaN semiconductor in its active layer, and also includes a surface-emitting semiconductor element for emitting laser light when excited with the excitation light source.
In a preferred form of the third color laser display, the surface-emitting semiconductor element of the semiconductor laser unit has an active layer composed of InGaAlP or InGaP, the semiconductor laser unit being employed as the red laser light source. The surface-emitting semiconductor element of the semiconductor laser unit may have an active layer composed of InGaN. In this case, the semiconductor laser unit is employed as the green laser light source and/or the blue laser light source. Moreover, it is preferable that the surface-emitting semiconductor element of the semiconductor laser unit have an active layer composed of GaN, GaNAs, or InGaNAs.
Furthermore, it is desirable that the semiconductor laser element (for the excitation light source) of the semiconductor laser unit of the third color laser display have an active layer composed of InGaN, GaNAs, or InGaNAs. It is also desirable that the semiconductor laser element of the semiconductor laser unit have a stripe width of 5 xcexcm or more.
In the color laser display of the present invention, an excitation solid laser unit with a Pr3+-doped solid-state laser crystal, or a fiber laser unit with a fiber having a Pr3+-doped core, or a semiconductor laser unit with a GaN semiconductor laser element for exciting a surface-emitting semiconductor element, is employed as a red laser light source, a green laser light source, or a blue laser light source. The red laser light, the green laser light, and the blue laser light, emitted from the light sources, are modulated based on red, green, and blue image signals and are projected onto the screen. Therefore, an image carrying these image signals can be displayed on the screen. With this construction, the color laser display of the present invention has the following advantages:
(1) The excitation solid laser unit, the fiber laser unit, and the semiconductor laser unit, employed as the red, green, or blue laser light source, do not require a cooling mechanism as does the conventional gas laser unit. Thus, the color laser display of the present invention is capable of sufficiently reducing the size, compared with the aforementioned conventional color laser displays. In addition, the reduction in the number of components results in a reduced cost. Even in comparison with the case of employing the aforementioned excitation SHG solid laser as a light source, the effect of the reduced cost by the reduction in the number of components is obtained because there is no need to employ a longitudinal mode control element, such as an optical wavelength conversion element, an etalon, etc.
(2) The light-to-light efficiency of the aforementioned excitation SHG solid laser unit is typically about 10 to 20%, whereas those of the excitation solid laser unit, fiber laser unit, and semiconductor laser unit of the present invention typically reach about 30 to 50%. Thus, the present invention is also capable of realizing high efficiency, compared with the conventional color laser display that employs the excitation SHG solid laser unit as the light source.
(3) The aforementioned excitation solid laser unit, fiber laser unit, and semiconductor laser unit of the present invention do not employ an optical wavelength conversion element in order to obtain a desired wavelength as does the excitation SHG solid laser unit. As a result, there is no occurrence of noise due to a conflict of longitudinal modes that results from wavelength conversion. Thus, the color laser display of the present invention is capable of suppressing an amount of noise to about less than 1%, for example.
(4) The GaN semiconductor laser element for excitation, employed in the color laser display of the present invention, is able to generate high output because its COD value (i.e., the maximum light output at the time of end-face destruction) is very high compared with other GaAs semiconductor laser elements, etc. This enables the color laser display of the present invention to display a high-brightness image.
(5) Particularly, the fiber laser unit employed in the second color laser display of the present invention is able to generate considerably high output as it does not have the problem of a thermal lens, etc. Thus, the second color laser display is capable of displaying a higher-brightness image.
(6) The color laser display of the present invention has the advantage that it can obtain modulated light by directly modulating the excitation GaN semiconductor laser element.